Conventionally, in order to contain leakage of liquid-state chemical substance from a reservoir, an enclosing wall is built on the ground to enclose the reservoir, defining a receiving space. However, the enclosing wall may prove a source of inconvenience when the reservoir is required to be replaced. In such cases, a to-be-replaced reservoir has to be lifted above the enclosing wall in order to be removed from the receiving space, and a new reservoir has to be lifted above the enclosing wall in order to be placed into the receiving space. In another case where the reservoir needs to be maintained, the person who is performing the maintenance has to climb over the enclosing wall, bringing along the necessary equipment.